The effects of lossy solvents on quantitative EPR studies

Abstract

To examine the correction factors which must be used to compare integrated EPR signal intensities in lossy solutions, we measured the effects of 12 solvents with different dielectric properties on cavity Q, resonant frequency, and integrated signal intensity. We also measured the effect of a quartz Dewar insert on these parameters. When the lossy sample was in a tube with an internal radius of 0.064 cm and the Dewar insert was present in the cavity, cavity Q and unsaturated integrated signal intensity decreased by up to a factor of 3, relative to the values for a nonlossy solvent at the same incident microwave power. The lens effect of the solvent increased the integrated signal intensity by up to 55%. The lens effect of the Dewar insert caused the integrated signal intensity to increase by a factor of 2.48. In the presence of the Dewar insert, cavity Q and resonant frequency were about 2.2 and 3.5 times more sensitive, respectively, to the changes in solvents ϵ′ and ϵ″ than those values in the absence of the Dewar. The lens effects of the solvents were about the same in the presence and absence of the Dewar.